Salarias fasciatus — Lawnmower Blenny
- For: hobbyists with mature tanks and live rock.
- Size: up to 13–14 cm.
- Real diet: detritivore–algae grazer; biofilm + nori/spirulina.
- Compatibility: peaceful; avoid mixing with conspecifics.
- Difficulty: medium; requires observation and vegetable supplementation.
A natural ally against filamentous algae and detritus in reef aquariums. Practical profile with real parameters, evidence-based feeding, and compatibility tips.
Introduction
Salarias fasciatus is a hardy blenny that scrapes biofilm, detritus and fine algae from rocks and glass. In young aquariums it may starve; in mature systems with live rock it becomes an excellent “groundskeeper”.
Experience — “When there’s microalgae and biofilm this fish works non‑stop; when there isn’t, help with quality vegetable foods.”
Identification & Taxonomy
| Field | Data |
|---|---|
| Scientific name | Salarias fasciatus (Bloch, 1786) |
| Family | Blenniidae |
| Common names | Lawnmower blenny, Jeweled blenny, Hairy blenny |
| Max size | ~13–14 cm |
| Distribution | Indo‑Pacific: shallow reefs, lagoons and flats |
Biotope & Behaviour
Inhabits lit rocky/reef areas, perching to graze and watch. Guards its immediate patch and can be brusque with similarly shaped fish (other blennies/gobies), while ignoring mid‑water species.
Experience — “Cover the tank: some individuals may jump during chases.”
Recommended Setups
Performs best in systems with live rock and sunny patches. In SPS/LPS reefs it ignores corals but may nibble nearby biofilm.
Water Parameters
| Parameter | Practical range | Notes |
|---|---|---|
| Temperature | 24–27 °C | Avoid spikes; stability first. |
| Salinity | 1.024–1.026 sg | Reef standard. |
| pH | 8.0–8.4 | Gentle daily swings are normal. |
| Nitrate | < 15 mg/L | Better 2–10 mg/L for biological stability. |
| Phosphate | < 0.1 mg/L | A little PO4 helps avoid “zero nutrients”. |
Feeding
Despite its “algae eater” nickname, evidence shows a mixed diet with a high fraction of detritus and microfauna alongside filamentous algae/diatoms. In mature tanks it often self‑sustains but should be supplemented.
Worked / Didn’t work — keep condition high
Worked
- Nori on a clip 1–2×/day.
- Pellets/flakes with spirulina and high plant content.
- Vegetable gel foods and blanched veg (zucchini/spinach) in small portions.
Didn’t work
- Relying on “clean rock” in ultra‑low nutrient tanks.
- Large, infrequent feedings → waste and apathy.
Doubting between fasciatus and ramosus? See the quick comparison
Compatibility
Peaceful with most reef fish. Can be territorial with other Salarias or similarly shaped blennies in small tanks. With corals: safe; may “perch” on colonies (Montipora/Porites) without harming them.
Comparison: Salarias fasciatus vs Salarias ramosus
Two similar algae‑grazing blennies in the trade. This table summarizes practical differences to choose for your tank.
| Feature | S. fasciatus | S. ramosus |
|---|---|---|
| Max size | 13–14 cm | ~10–11 cm |
| Coloration | Mottled brown/green; marked head cirri | More regular pale spotting |
| Natural diet | Detritivore‑algae grazer (biofilm, filaments, microfauna) | More algae‑dependent; visible algae |
| Temperament | Territorial with conspecifics/similar blennies | Slightly more tolerant |
| Best for | Mature systems with live rock and biofilm | Medium tanks needing extra algae control |
| Difficulty | Medium (needs veg supplement) | Medium‑low (if algae is available) |
Experience — “If your tank is mature and you want a very active fish: fasciatus. If you prefer smaller and visibly algae‑focused: ramosus.”
BCS — Body Condition Score
Quick guide to assess if your Salarias is keeping good condition. Use the belly line and fullness of flanks as reference.
BCS 1 — Thin
Critical
- Sunken belly, concave flanks.
- Erratic pecking or apathy.
Action: daily nori + veg gel; reduce competition.
BCS 2 — Low
Needs improvement
- Ventral line straight or slightly concave.
- Active grazer but tires quickly.
Action: add 1–2 small veg feedings.
BCS 3 — Good
Target
- Flat to slightly convex belly.
- Steady pecking, normal behaviour.
Action: keep routine and stability.
BCS 4 — High
Monitor
- Very convex abdomen; fat visible.
- Lower activity.
Action: cut fatty pellets; prioritise veg fibre.
Myths vs Facts
| Myth | Fact | What to do |
|---|---|---|
| “It only eats algae.” | Mixed diet with lots of biofilm/detritus. | Daily nori/spirulina in small servings. |
| “If there’s algae, that’s enough.” | Visible algae ≠ sufficient nutrition. | Watch BCS and adjust supplementation. |
| “It nips corals.” | Mainly perches; rarely nips polyps. | Provide perches and resting flats. |
Compatibility (in the tank)
| Group | Compatibility | Notes |
|---|---|---|
| Clownfish | High | They ignore the blenny. |
| Gobies/blennies | Medium | Similar shape → disputes. |
| Other Salarias | Low | Only in large tanks with many hides. |
| Herbivorous tangs | Medium | Pasture competition; add nori. |
| SPS/LPS corals | High | Perches without damaging. |
Express Buying Guide
Signs of good condition
- Flat/slightly convex belly (BCS ≥ 3).
- Constant pecking on glass/rock in the shop tank.
- Clear eyes, intact fins, reacts when you approach.
- Accepts nori/spirulina pellets in a quick test.
When NOT to buy
- Sunken belly and concave flanks (BCS 1–2).
- Apathetic, sitting on the bottom without grazing.
- Wounds on chin/mouth or erosion around lips.
- Shop tank “too clean” with no visible biofilm.
Risk of Weight Loss — Estimator
Tick what applies to your tank and count ✓.
| # | Statement | Applies? |
|---|---|---|
| 1 | Volume < 150 L. | |
| 2 | Live rock < 8% of volume (under 8 kg per 100 L). | |
| 3 | System age < 4 months. | |
| 4 | Herbivore competitors ≥ 2 (tangs, other blennies, etc.). | |
| 5 | Vegetable supplement currently 0 times/day. |
Interpretation: 0–1 ✓ = Low · 2–3 ✓ = Medium · 4–5 ✓ = High.
Quick Glossary
Biofilm
Thin layer of microorganisms and detritus coating rocks/glass; a key food.
Diatoms
Early brown microalgae; useful for start‑up grazing.
Perches
Flat spots (e.g., Montipora plates/rock) where the blenny rests to watch.
Breeding (overview)
Demersal, adhesive eggs laid in cavities/crevices; males often guard. Planktonic larvae drift before settlement. In captivity, sporadic reports; needs hides and live microfoods after hatch.
Health
The most common issue is loss of condition due to lack of biofilm/algae. Opportunistic infections may appear if there are mouth abrasions. Prevention: stable water, sufficient diet, and quarantine.
| Situation | Signs | What to do |
|---|---|---|
| Weight loss | Sunken abdomen | Increase veg foods (nori/spirulina) and reduce competition. |
| Territorial stress | Chases with other blennies | Rescape and add hides; consider separating individuals. |
| Mouth abrasions | Marks on mouth/chin | Improve water quality; watch for infection. |
Common Mistakes
- Don’t add to brand‑new tanks without biofilm.
- Don’t mix with other Salarias in small tanks.
- Don’t assume “only algae”: needs varied, fibre‑rich diet.
Scientific Evidence (2018–2025)
Diet & feeding morphology
- Natural diet includes detritus, diatoms, microfauna and an algal fraction; comb‑like dentition scrapes substrates. J. Fish Biology
- Taxonomic and regional summaries for combtooth blennies; practical anchor to understand grazing behaviour. ScienceDirect Topic
Health & biosecurity (general ornamental context)
- Columnaris complex and resistance trends; importance of hygiene & probiotics as adjuncts. J Fish Diseases, 2025
- Aquatic animal health resources and antimicrobial stewardship. FAO · WOAH Compendium
Further Reading
- AtlasReef articles on reef husbandry and algae management.
- Community case studies (e.g., PasionReef) with long‑term blenny care.
FAQ
Will it clear all algae?
No. Think of it as a helper. Combine with nutrient control and manual removal.
Can I keep two lawnmower blennies?
Only in large tanks with many hides; otherwise expect fights.
Does it eat prepared foods?
Many accept spirulina pellets and nori after acclimation; offer small, frequent servings.
Reef‑safe?
Yes for corals; it perches on colonies without damaging polyps in most cases.
Minimum tank size?
From ~150 L with mature rock and steady nutrient regime.